Novel C-MOS compatible monolithic silicon gas flow sensor with porous silicon thermal isolation

A novel C-MOS compatible silicon gas flow sensor using porous silicon for thermal isolation has been designed and fabricated. The small sensor size combined with the very good thermal isolation by porous silicon assure fast response, with a time constant of the order of 1.5 ms. The principle of operation is based on heat transfer from a polysilicon resistor to the fluid and the detection of the flow-induced temperature difference by A1/polysilicon thermopiles, integrated at both sides of the heater. The sensor has been evaluated in nitrogen flows from 0 to 0.4 m/s. The sensitivity per heating power is 6.0 mV/(m/s)W and the responsivity is 0.65 V/W. The noise equivalent power and the minimum detectable velocity are 1.5 X 10(-8) W/Hz(1/2) and 4.1 X 10(-3) m/s, respectively. The chip size is 1.1 mm X 1.5 mm. (C) 1999 Elsevier Science S.A. All rights reserved.